Android is great if you are on a budget and can't purchase other operating systems for mobile devices. It is also great for installing third-party apps if you find one you like. Although there is a lot of customization options available, this may cause some users to become frustrated if they are unfamiliar with this system.
FreeNAS is well suited for most storage serving scenarios, whether it be for an office file server, backup destinations, data replication across the internet, or as backend storage for virtual machines. It can serve various types of clients via a plethora of standard protocols and can easily integrate with existing infrastructure using LDAP authentication and so on. It's pretty simple to use (it helps to have at least a basic understanding of the underlying technologies) and almost maintenance-free. One scenario that springs to mind that it may not be appropriate for (yet) is as S3 storage. However, S3 functionality was added in a recent release and may have improved greatly since then. I'm sure it will eventually work very well for this.
These two operating systems are both great and can totally do everything that we need in our school. The reason we go with Android is that it is cheaper and we have a greater variety of apps available to us. iOS can be a little pricey and it also doesn't allow us to do the customization that we want.
FreeNAS effectively uses all resources really well and it is highly recommended for in premises NAS. It has unlimited ROI as it is really free and open-source. The only payment we need to pay is when we need any support from those guys. FreeNAS helps us to effectively do our work with the legacy systems as it manages all the components really well. FreeNAS although rebranded to TrueNAS will still be there until our legacy systems run.